Hydration inhibitor coating for adhesive bonds

ABSTRACT

An adhesively bonded article includes a metallic substrate that has an oxide layer thereon, a phosphonate bond promoter coating on the oxide layer, an adhesive material on the bond promoter coating, and a component bonded to the metallic substrate by way of the adhesive material.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.12/870,892, filed Aug. 30, 2010.

BACKGROUND

This disclosure relates to adhesively bonded joints. Assembledcomponents, such as aircraft components, may utilize an adhesivematerial to hold two or more sub-components together. Typically, atleast one of the sub-components is metallic. A primer layer may beapplied to at least one of the sub-components to help form a strongbond. The primer layer may contain hexavalent chromium to protect themetallic sub-component from corrosion and provide a strong bond.

SUMMARY

An example adhesively bonded article according to an example of thisdisclosure includes a metallic substrate that has an oxide layerthereon, a phosphonate bond promoter coating on the oxide layer, anadhesive material on the bond promoter coating, and a component bondedto the metallic substrate by way of the adhesive material.

In a further example of any of the forgoing examples, the metallicsubstrate is an aluminum alloy.

In a further example of any of the forgoing examples, the bond promotercoating is a monolayer.

In a further example of any of the forgoing examples, the adhesivematerial is epoxy.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the disclosed examples willbecome apparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

FIG. 1 illustrates an example adhesively bonded article.

FIG. 2 illustrates an example method for adhesively bondingsub-components together to form an adhesively bonded article.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates selected portions of an example adhesively bondedarticle 20. The adhesively bonded article 20 is not limited to anyparticular kind of article. In one example, the adhesively bondedarticle 20 may be an aircraft component that has a composite structure.The composite structure may be a honeycomb composite that includes twosheets and a honeycomb material bonded between the sheets.

In the illustrated example, the adhesively bonded article 20 includes afirst sub-component 22 and a second sub-component 24 that is adhesivelybonded to the first sub-component 22. In this regard the sub-components22 and 24 are not limited to any particular kind. For example, the firstsub-component 22 is a metallic substrate, such as a sheet of aluminumalloy. The aluminum alloy may be aluminum 2xxx, aluminum 5xxx, aluminum3XXX, aluminum 6xxx, aluminum 7xxx, or other desirable aluminum alloycomposition. Likewise, the second sub-component 24 is not limited to anyparticular type of sub-component. In the case of a honeycomb composite,the second sub-component 24 may be a honeycomb material that is bondedto the metallic substrate.

The first-subcomponent 22 includes an oxide layer 26 that is located atleast on the surface of the first-subcomponent 22 that is to be bondedto the second sub-component 24. The oxide layer 26 may be an oxide of anelement or elements that form the metallic substrate. For instance, theoxide layer 26 may be aluminum oxide, where the aluminum in the oxide isfrom the aluminum alloy of the first-subcomponent 22.

The adhesively bonded article 20 also includes a bond promoter coating28, which is also considered to be a barrier coating, between the oxidelayer 26 and an adhesive material 30. The bond promoter coating 28 maybe a phosphonate conversion coating that functions to resist hydrationof the oxide layer 26. As will be described below, the bond promotercoating 28 may be formed by treating the oxide layer 26 with aconversion coating solution. In this regard, the bond promoter coating28 may be a derivative of the selected conversion coating solution. Insome examples, the bond promoter coating 28 is a monolayer coating. Themonolayer coating has a unitary molecular thickness and is generally 100angstroms or less in thickness. The adhesive material 30 may be epoxy orother type of polymeric material that is suitable for bonding the firstsub-component 22 and the second sub-component 24 together.

The oxide layer 26 can adsorb moisture from the adhesive material 30.The moisture can hydrate the oxide layer 26 and convert the oxide layer26 (e.g., Al₂O₃) into less desirable types of oxides. For instance,aluminum oxide can hydrate to AlOOH (oxyhydroxide boehmite), Al(OH)₃(bayerite), other oxide phases, or combinations thereof that exhibitweaker bonds with the underlying metallic substrate and thereby weakenthe bond strength between the first sub-component 22 and the secondsub-component 24. However, in the disclosed examples, the bond promotercoating 28 resists hydration of the oxide layer 26 to thereby provide astronger and more durable bond between the first sub-component 22 andthe second sub-component 24.

FIG. 2 illustrates an example method 40 for adhesively bonding ametallic substrate and a component together. For instance, the method 40may be used to fabricate the adhesively bonded article 20 as describedabove. In the illustrated example, the method 40 includes steps 42, 44,and 46. Step 42 includes treating the metallic substrate to form theoxide layer 26 thereon. Step 44 includes treating the oxide layer 26with a conversion coating solution to form the bond promoter coating 28on the oxide layer 26, and step 46 includes depositing the adhesivematerial 30 on the bond promoter coating 28 to bond the metallicsubstrate (first sub-component 22) and the second sub-component 24together.

Step 42 may include anodizing the metallic substrate to form the oxidelayer 26. The anodizing may be conducted in a known manner using asuitable anodizing solution. For instance, the anodizing solution may besulfuric acid, phosphoric acid, organic acid, boric acid, chromic acidor combinations thereof, but the anodizing solution is not limited tothese examples. A few examples of organic acids include malic acid,sulphonated aromatic acids, sulfosalicylic acid, oxalic acid, tartaricacid, or combinations thereof. Alternatively, step 42 includes naturallyforming the oxide layer 26 on the metallic substrate by exposing themetallic substrate to air. The oxidation may be accelerated with theapplication of heat and exposure to air or other oxidizing gas.

Step 44 includes treating the oxide layer 26 with a conversion coatingsolution to form the bond promoter coating 28 on the oxide layer 26. Thetype of conversion coating solution that a user selects may depend uponthe type of bond promoter coating 28 that the user desires to form. Forexample, the conversion coating solution may include trivalent chromiumand phosphonic acid. The phosphonic acid may be nitrilotris (methyelene)triphosphonic acid. Additionally, the parameters of the conversioncoating process, such as the composition of the conversion coatingsolution and the treatment time may be controlled in a known manner toform the bond promoter coating 28 as a monolayer bather coating on theoxide layer 26. In this regard, the composition of the monolayer bathercoating depends upon the composition of the conversion coating solution.For the above phosphonic acid conversion coating solution, the monolayerbather coating is a phosphonate monolayer and functions as describedabove to resist or limit hydration of the underlying oxide layer 26. Thebond promoter coating 28 thereby functions to decrease or reduce therate of water diffusion from the adhesive material 30 into the oxidelayer 26.

Step 46 may include depositing the adhesive material 30 onto the bondpromoter coating 28, the second sub-component 24, or both to bond thefirst sub-component 22 and the second sub-component 24 together. In thisregard, the depositing of the adhesive material may include a knowntechnique, such as spraying, painting, depositing by syringe, or otherknown technique. Depending on the type of adhesive material 30 that auser selects, an additional step of curing the adhesive may follow step46. Given this description, one of ordinary skill in the art willrecognize other steps that may be used in combination with the describedmethod 40 to suit their particular needs, either prior to, in between,or subsequent to the steps 42, 44, and 46.

Although a combination of features is shown in the illustrated examples,not all of them need to be combined to realize the benefits of variousembodiments of this disclosure. In other words, a system designedaccording to an embodiment of this disclosure will not necessarilyinclude all of the features shown in any one of the Figures or all ofthe portions schematically shown in the Figures. Moreover, selectedfeatures of one example embodiment may be combined with selectedfeatures of other example embodiments.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this disclosure. The scope of legal protection given tothis disclosure can only be determined by studying the following claims.

What is claimed is:
 1. An adhesively bonded article comprising: ametallic substrate having an oxide layer thereon; a phosphonate bondpromoter coating on the oxide layer; an adhesive material on the bondpromoter coating; and a component bonded to the metallic substrate byway of the adhesive material.
 2. The adhesively bonded article asrecited in claim 1, wherein the metallic substrate is an aluminum alloy.3. The adhesively bonded article as recited in claim 1, wherein the bondpromoter coating is a monolayer.
 4. The adhesively bonded article asrecited in claim 1, wherein the adhesive material is polymeric.
 5. Theadhesively bonded article as recited in claim 1, wherein the adhesivematerial is epoxy.
 6. The adhesively bonded article as recited in claim1, wherein the metallic substrate is an aluminum alloy and the oxidelayer is aluminum oxide.
 7. The adhesively bonded article as recited inclaim 1, wherein the component includes a honeycomb material.
 8. Theadhesively bonded article as recited in claim 1, wherein the metallicsubstrate is a sheet.
 9. The adhesively bonded article as recited inclaim 1, wherein the metallic substrate is an aluminum alloy sheet.